1. Field of the Invention
The present invention relates to the preparation of esters of .beta., .gamma.-unsaturated carboxylic acids by the carbonylation of conjugated dienes with carbon monoxide, in the presence of an alcohol, a halogenated hydracid and a palladium catalyst, with recovery and recycling of the said catalyst.
2. Description of the Prior Art
It is known to this art, from Japanese Patent No. 48.5564, to prepare monoesters of .beta., .gamma.-unsaturated carboxylic acids by the carbonylation of conjugated dienes with carbon monoxide, in the presence of a monoalcohol, a non-halogenated palladium catalyst and a halogenated hydracid, at a temperature on the order of 100.degree. C. and under a carbon monoxide pressure on the order of 100 bars; the patent is silent regarding any method for recovering the catalyst.
It has also been shown, per French Patent Application No. 81/01,205, filed Jan. 23, 1981, and assigned to the assignee hereof, that the selectivity in respect of the desired esters, the degree of conversion of the conjugated dienes employed and the stability of the palladium catalyst are improved if the medium subjected to carbonylation also contains a quaternary onium salt of an element of Group VB of the Periodic Table selected from among nitrogen, phosphorus and arsenic, and comprising an anion selected from among "hard" or "intermediate" bases [according to the definition set forth by R. Pearson in J. Chem. Ed., 45, 581-7 (1968)].
Also, the said application does not indicate how to recover the palladium catalyst for the purpose of recycling it.